text:
Why is radio communication still used?
Why is radio still the method of communication from the ground to air? If i'm not mistaken, cellular services should be much better in quality and reliability

Cellular towers have a very limited range, and are not usually tuned to point up into the air. They are also poorly equipped to handle multiple frequencies, I'd hate to have a single cellular frequency for every transmission, you'd never get a word in. They are also prone to issues with congestion, the more users a tower has, the lower the quality of service.

Very similar, if not an actual dupe

Related: https://aviation.stackexchange.com/questions/36074/is-there-a-solution-to-radio-interference/

Perhaps this is being pedantic, but cellular services are also radio.

So you are kind of asking why not use some advanced modulation and protocol like GSM (or Project 25?) but just FM analog voice radio. For the same reason your alarm clock still use 1.5V battery: legacy, too expensive to change the whole system.

@user3528438 Aviation voice communications in the 108-136 MHz band is actually AM (amplitude modulation).

"should be much better in quality and reliability" - why? if you can explain why you believe this, you'll get more helpful answers

"should be much better in quality and reliability"  Have you ever had a dropped cell phone call?  Have you ever had a dropped AM transmission?  I'd say AM is more reliable!

Can be nice to have a lot of celular antenas scatered over the OCEAN

Note that CPDLC has already been implemented in some places and will be expanding over the next several years

@jean: Or even places like California's Sierra Nevada and its "Empty Quarter" north of Susanville, or just about anywhere in the Great Basin outside actual towns. Then there's a lot of Canada and Alaska...

When I fisrt read the question, I imagined it would be about text (ACARS, CPDLC) vs voice (AM radio) and not AM radio vs cell-phones

I'm enjoying FM stations on the car radio. Old technology that still works very well, good sound quality.

Cellular communication has multiple issues:

When a plane is up more than a few thousand feet, a cell phone would see, and try to talk to, multiple cell towers at once.  At best, this is inefficient and overloads the cell network.  At worst, the network can get confused and drop calls.  (not something you want when trying to get ATC directions)
When a plane is moving rapidly, it will change cell towers frequently.  This has the same problems as above.
Cell communications is designed for Person-to-Person during a single call.   Aviation radio is designed so that everyone can hear everyone else's communications.  Even if an ATC instruction is not specifically for me, I can get a mental picture of what other planes are nearby and what they are doing.  This is not so easy with cellular.
In many rural areas, cell phone coverage is limited.

And the GSM-Standards are rather fast moving targets. We are now looking ahead for 5G and some states are already shutding down 2G. But planes get much older, imagine a A320 from 1987 or 747-400 from 1989, 2G wasn't even available at that time. For the same reasons I would avoid integration of such short living proprietary standards like CarPlay or Google Auto. Sticking with something reliable which you can control yourself, at least they can reach ATC at New Years Eve...

@Peter: How about a Piper Cherokee from 1965?  And there are older planes than that being flown regularly.

I think there would be some issues convincing people to fit such technology into a spitfire or any other WWII aircraft for that matter!

@jamesqf older aircraft are retrofitted with modern equipment all the time. Just because older tech exists doesn't have to mean new tech can't be introduced (heck, we're not looking at mandatory introduction of collision avoidance systems in all aircraft, down to warbirds).

@jwenting: Sure, but that newer equipment is generally backwards compatible with the old.  Replacing the old tube-type navcom in the Cherokee with a newer solid-state unit didn't change anything major,

As mentioned in comments radiocommunication includes all forms of radio links, hence includes cellular networks.
Cell size
A cellular network covering any land is not realistic, not mentioning water areas. Given the size of a cell, at most 20 km for GSM (1G/2G), and much less for UMTS/LTE (3G), this would lead to prohibitive costs:

Continents represent about 150 millions km², a GSM cell covers about 10 km² (in large cities a cell usually covers less than 1 km²).
15 millions cells would be required, still lands are only 30% of Earth's area.

User's motion speed
If we used the existing cellular network, the current cell size would be impractical for fast mobiles.

Handoff, source
With small cells, fast users would constantly hop (handoff) from a cell to another. The network would be overloaded and the efficiency of the mobile node would also decrease a lot as cell transfer has some overhead, including frame replication by all cells in sight. Actually an assumption for the design of a phone cellular network is infrequent handoffs during a communication.
A more suited size would be about 100+ km, which is impossible in urban areas due to cells overlapping to try cover shadowed areas.
GSM and UMTS standards limit user's equipment power to 2 W (33 dBm) and 125 mW (21 dBm) respectively.
If the cell size is increased this power must be increased too (see here a link budget for UMTS). Each time the cell size doubles, the power used must be be multiplied by 4. As @jamesqf pointed out, the cell size impacts the phone set running time. The user's equipment would need larger batteries to maintain the same running time, or the running time would be divided by 4 each time the cell size doubles.
If the cell size is increased, there are more users in the same cell. The combination more users + more power would need important changes in the cellular network technology to prevent interferences.
3D coverage
Current antennas are oriented towards ground for efficiency and noise reduction. In practical a base station is barely reachable by an aircraft flying at 10 km altitude.

Source
We would need a 180° beam versus the current 10° beam. As the cell is now a cube instead of a disc, power must be increased to reach the top corners, which can be done at the price of increasing cell overlap at ground level and higher cross-cell interference.
Further reading
There is a master thesis on this exact topic:

Feasibility study of a WCDMA direct air-to-ground link in the UMTS licensed band, by Dora Swamy Naidu Raghavarapu.

From the section Conclusions and Outlook:

[...] Some aircraft specific constraints, such as Doppler shift,
  propagation delay, handover and interference have been identified and
  analyzed. Doppler shift occurs in terrestrial networks on a much
  smaller scale, since mobile stations on the ground move at much lower
  speeds. However, WCDMA receivers are equipped with powerful frequency
  acquisition circuits, capable of counteracting this effect. We have
  also shown that propagation delay has no significant effect on the
  power control mechanism. Finally, we have seen how UMTS networks can
  perform handover procedures between remote parts of the network.
[...] we have focused much of our study on analyzing the possibility
  of using UMTS terrestrial frequencies for an aircraft component. It
  can be observed from the simulation results shown in chapter(6), that
  an aircraft component transmitting at these frequencies would degrade
  the performance of the existing network to an intolerable extent due
  to interference.
[...] In order for the aircraft to degrade the performance of the
  terrestrial network only to a tolerable extent, it would need to
  transmit at extremely low power. The airspace cells would then have to
  be so small that the system would be impractical.

Future solution is already broadly defined and satellite-based
Using the phone cell network is impractical, and has few advantages over other solutions. If a radio network had to be build for aviation, it would be a satellite one to cover oceans. It would be cheaper (relative) than building an equivalent on the ground.
Could such satellite network be built in spite of its cost? Well, it is already under construction!
The need for constant radio exchanges between aircraft and ground has increased a lot since 15 years:

ACARS can already use satellites, and it's a matter of choice for an airline to use this kind of link in addition of VHF/HF.
Airlines start to offer Internet access in flight. Wi-Fi access points are installed in the cabin and the local traffic is routed to a satellite which relays it to a ground station connected to the Internet.
Airlines also start to allow cellular phones in flight, using the same satellite technology.
ATC systems are currently redesigned (NextGen in the US, SESAR in the EU) to move from ATC ground-based links to ATC satellite-based links.

Source
In this numeric world, ATC voice communication is just another data flow, very small compared to ACARS, Wi-Fi and cell phone. There will be little difficulty to reuse data channels for voice transfer, just like IP phones have replaced traditional fixed phones in countries with a broadband Internet backbone.

Another factor in using current cell technology with widely-spaced towers is the power requirement for phones.  Think your battery life is bad now?  Wait until you try to talk to a tower 100 km away.

Yeah, there's another factor.  Double the range of your tower, and you square the number of phones that are likely to be in that area.  And probably increase the chances of a higher peak load more than that.

Original GSM bands when introduced in Europe allowed for a max range of about 50km. Which shows another problem, which of the many GSM bands are you going to use and support? There are multiple, causing most modern cell phones to need to have hardware to send and receive on 2-3 at them at least.

GSM only works for a relative speed between the handset and the base station of 250 kph max (130 kph max for 1800 MHz). UMTS is slightly better, but it too maxes out at 500 kph. Many planes fly faster than that. Airliners regularly cruise at 800 kph+ groundspeed, with a nice tailwind, they may achieve 1000 kph. That's twice as fast as the maximum possible relative speed for UMTS, and almost 8 times faster than the maximum possible relative speed for GSM 1800 MHz.

@mins, it depends on the density of the cells. In area with many cells there will be reachable cell below and the hand-off will be the biggest issue. But when the next cells is 20 km ahead, you won't be able to contact it due to the speed. So it can be a factor depending on the network layout.


text:
Why are some Tomahawk missiles' nose duck-nose shaped?
Why there is a duck-like shape in this Tomahawk missile's nose?  I see this shape in most Tomahawk images; however, not every Tomahawk's nose is shaped like this.  If it is an aerodynamic feature, what is its common name?

I developed the shape for Convair back in the late 90's.  It was called a chined nose and Carlo is right, there were no aero considerations for this shape.  It was purely RCS.

Hello and welcome! While this really should be a comment on Carlo's answer, I'm giving you an up vote so you can start earning enough rep to be able to make comments where appropriate. In the meantime, please take the [tour] and read through the [help] so you can get the most out of the site. Hope you stick around - that's the kind of background and knowledge that's absolutely invaluable 'round these parts!

It’s a feature on the latest variants of the Tomahawk to reduce its frontal radar cross section.  It has no aerodynamic role for the weapon.

Hello! The last sentence is a bit irrational. A geometric shape definitely has an aerodynamic role, be it a small contribution towards stability/performance or a large one.

I think what is meant is that any beneficial or detrimental contribution to the missile‘s aerodynamics and flight mechanics was tolerated in order to achieve the radar cross section objective.

Meaning that shaping is not necessary for aerodynamic reasons and is added for low observability enhancement only.

source: Stack Exchange

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

sort: votes


text:
Are landing fees due for an aborted landing in USA?
Suppose I receive landing clearance for an airport that charges a landing fee, and begin my decent. Then, for some reason I have to abort the landing and instead of going around and landing there I change my plans and wish to depart the airspace. Will I be liable for any landing fees if my wheels haven’t touched the runway at such airport?
I am asking for GA in the USA.

I commuted to work in my plane into an airport with a landing fee for a few years (I was doing it frequently enough that I paid for an annual subscription with unlimited landings). In Canada you won't be charged if you go around and I can't imagine being charged in the US either.  Although ATC records the landing, the fee is usually levied by the airport authority and is intended to cover airport services, not ATC services.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
Is a reversal of heading allowed in the NYC Hudson VFR corridor?
The special rules chart indicates that northbound traffic should follow the eastern edge of the Hudson and southbound should follow the west one.
Suppose a pilot wanted to only go mid-way through the corridor and then turn back, would it be allowed to make a 180 turn, merge into the traffic along the opposite edge, and simply go back?

I've never flown the corridor myself but from what I can find online it looks like a U-turn would be a case of "legal but not safe". 14 CFR 93.350 defines two different types of traffic in the SFRA and the FAA's kneeboard guide has a 'plain English' summary:

Fly in proper altitude range

Transient operation* [1,000 ft up to, not including, 1,300 ft MSL]
Local operation** [Surface up to, not including, 1,000 ft MSL]

It also explains what those operations are (emphasis mine):

Transient operation: Aircraft transiting the Hudson River Exclusion from end to end without intending to signicantly [sic] change heading, altitude, or airspeed.
  Local operation: Any aircraft within the Hudson River Exclusion that is conducting an operation other than overflying.

Those definitions certainly seem to allow for turns and maneuvering as part of "local operations". However, as Dave pointed out, the corridor is very narrow and maneuvers in a fixed-wing aircraft might be risky. In fact, there's already been one high-profile accident in the East River corridor where the aircraft hit a building after trying to a make a tight U-turn in a strong wind. I suspect that most aircraft maneuvering actively in the SFRA are probably helicopters rather than fixed-wing airplanes.
If you search newsgroups and forums about this you'll find a lot of comments about helicopter traffic at very low altitudes, and many pilots say that turning in the Hudson River corridor isn't a great idea. This thread is a good example.
The FAA has a safety course for the SFRA, by the way. I haven't done it but it might have more information.

There is nothing on the supplement that specifically excludes it but the supplement specifically states

...while remaining within the boundaries of the Hudson river exclusion

On the charts I'm seeing distances between 0.7 NM and 0.8 NM for the width of the river around that area. That is a fairly tight distance to execute a 180 in some aircraft and should something go wrong a maneuver like this would not play out in your favor.
The supplement also contains directional arrows none of which show an area to turn around.
I would say as it stands its allowed but perhaps, ill advised.

Isn't that what happened to Cory Lidle? He tried to make a 180 in the corridor but went too wide and hit a building.


text:
What are the considerations for coding the GPS before engine start without external power?
Suppose I would need 10-15 minutes to fully configure my G1000 on a C172 ahead of a flight, with the flight plan, my personal view settings, etc., and prefer to do that before starting the engine. My goal is to save fuel, save hobbs/tach time, and reduce deposits accumulating on the spark plugs.
What would be the considerations against doing that on battery power alone? And what can I do to reduce the impact of any downsides?

15 minutes is a long time to be draining the battery, it's not just the G1000 that will be running but the electronic gyros, beacon, etc. If the airplane hasn't been recently flown and it's cold outside 15 minutes may be long enough that you can't crank your engine.
There's also problems with running the G1000 while starting the engine:

It's not good for the electronics: you get all sorts of electronic noise and surges when running the starter. I don't think it's that much of a problem with modern electronics, but the G1000 is a painfully expensive piece of equipment and you want to preserve it in any way you possibly can!
You get a power sag: the starter drains a lot of power, there may not be enough to keep the G1000 going and it may restart. It it restarts you lose all that configuration you did! You could mitigate that by saving your flight plan to an SD card, shutting down the avionics for start, then re-loading it

The last issue is that 15 minutes is time you could be flying, or someone else could be flying. It's also time you might be paying for depending on the school or group you rent from (if you rent)
There's no reason to do this anyway to be honest, you can use SkyVector, Foreflight, SkyDemon, Garmin Pilot and other flight planning software to plan your flight on a tablet or other computer, load onto an SD card, then load it on to the G1000. Some of the software costs money but it's worth every penny as it gives you the opportunity to take your time planning flights rather than rushing to get waypoints in. The interfaces are also much nicer to use than the G1000.

Garmin also makes a G1000 simulator so you can practice making adjustments, etc on your computer so you can do it more quickly once you start the plane.


text:
Traversing a tall suspension bridge during low overcast
Suppose a pilot is flying VFR with excellent visibility and calm wind but with a ceiling of 1000, along a wide river at 500 feet. At some point she approaches a suspension bridge. Climbing and trying to cross in between pillars would be illegal due to getting too close to the clouds.
Now, would it be illegal and/or be considered excessively hazardous to fly under the bridge assuming that the vertical clearance above the river is around 300 feet?

But one needs to be 500' above the Gnd unless landing.

And also closely related

Not when one is not over populated areas, such as over extensive bodies of water

But typically there are boats on the water, those also need to be avoided by 500'.

So you need to be 500' below the bridge, and 500' away from the water just to confirm you are 500' clear of things, so 300' is not legit.

You're assuming there are boats.  The question does not mention their presence.

Doesn't say there aren't any either.

Sounds pretty hazardous (and almost definitely illegal) to me
Here's the first photo of the first suspension bridge I found when I looked on Wikipedia

Guy Wires
Can you see all the really narrow guy wires below the bridge?  No?  I can't either.  If you can't see them in a photo, how are you going to see them at 100 knots?
"But Steve, maybe there aren't any!"
Yes, or maybe there are.  Are you confident enough to bet your life on it?
I thought you were the one with the plan!

Each pilot in command shall, before beginning a flight, become
familiar with all available information concerning that flight. (FAR 91.103)

Suspension bridges aren't like TFRs, they don't just appear in between the time you took off and the time you get to them.  Why didn't you know there was a bridge there before you took off?  Why didn't you have a plan for what to do when you got there already?
Boats are people too
You need to stay 500 feet from any structure.  Bridges are structures, so you need to be 500 feet away from them.  You also need to be 500 feet away from vessels and people, so if there's anyone on the river, your options just went from "bad" to "none".
But what about my emeeeergency?
All the rules go out the window if you're experiencing an emergency...as long as you're acting in the interests of the safety of the flight.  I spent some time on a foggy morning talking with an FAA inspector about this very topic (flying under bridges in emergencies) a couple years ago, and his words were to the effect of:

"It would have to be a very unique emergency for flying under a
bridge to be the safest course of action."

"Why didn't you know there was a bridge there before you took off?"  This.

Excellent answer.  Just one question, what guy wires are there underneath a suspension bridge?  By definition, (and in accordance with the law of gravity) a suspension bridge is suspended by guy wires from above.

P.S.  The bridge pictured is a bizarre looking hybrid of a suspension bridge, and one supported from beneath by arches.  In either case though, below ought to be clear if you really needed to go there...

@MichaelHall - If I was a bridge-ineer instead of a plane-xecutive I would probably know facts like that.  I'm not willing to bet my life on there being no wires down there, though.

@MichaelHall. It's an arc bridge, not a suspension bridge. The 'suspension part' of the hybrid you mention is only a temporary structure erected in order to facilitate the construction work of the central sections.

Still, to the answerer's point, there could be random steel cables whipped around under there like the spider web between my car and my neighbor's truck that I get face-wrapped by every morning when I go to work.  I am not a bridge designer either, but maybe the extra tension from such wires that could be there might provide stability to the structure.  Again, do you bet your life?  If it is an emergency, then set your eyes on the attitude indicator and climb.

@xxavier, the two towers in the middle are a temporary structures to support constructing the middle, but there are some suspension wires above the already complete parts that look permanent, so it does look like an arch-suspension hybrid.

@Jan Hudec   No... It's no hybrid... It's the Whirlpool Rapids Bridge, a pure arch bridge. The towers seen in the picture of the bridge under construction are either temporary towers, or parts of the previous suspension bridge, the 'Niagara Falls Suspension Bridge', that were used to facilitate the construction of the arch bridge and temporarily preserve the traffic, being destroyed at its completion.

I'm getting "bridgucated" here!  Good stuff though...  Two final comments:  1. Probably not the best photo to show someone an example of a suspension bridge.  2.  The only type of bridge I know that uses guy wires anchored downward through the water are floating bridges, and you definitely don't want to try to fly under one of them!

Yes, it is illegal.  Regardless of where you are, you are required to remain at least 500’ from any person, building, structure, or vessel.
Unless you are operating in Class G airspace, it’s also illegal, as you really don’t meet the weather requirements for VFR flight, either.
Don’t try it.  People get killed doing scud running like that all the time.

I have never heard this called "acid running".  I am very curious though.

I'm betting that whatever autocorrect @Carlo used didn't recognize "scud" and helpfully changed it to "acid"

@SteveV. - Yeah... I got a good chuckle out of this once I realized you're right.


text:
Is required that your alternate airport has approaches other than GPS approach?
I start to read AIM and AC90-105A about alternate considerations.If I have GPS(TSO-129 let’s say),Can I file based on a GPS-based IAP at the alternate airport,and my alternate airport only has GPS approach?

https://www.faa.gov/documentLibrary/media/Advisory_Circular/AC_90-105A.pdf#page28

See 9.5 of the referenced document:

9.5 Contingency Planning for Alternate Airport.
  9.5.1 Alternate Airport Considerations. For the purposes of flight planning, any required alternate airport must have an available instrument approach procedure (IAP) that does not require the use of GPS. This restriction includes conducting a conventional approach at the alternate airport using a substitute means of navigation that is based upon the use of GPS. For example, these restrictions would apply when planning to use GPS equipment as a substitute means of navigation for an out-of-service very high frequency omni-directional range (VOR) that supports an instrument landing system (ILS) Missed Approach Procedure (MAP) at an alternate airport. In this case, some other approach not reliant upon the use of GPS must be available. This restriction does not apply to pilots
  with navigation systems meeting the requirements below.
9.5.1.1 For flight planning purposes, TSO-C129( ) and TSO-C196( ) equipped users (GPS users) whose navigation systems have fault detection and exclusion
  (FDE) capability, who perform a preflight RAIM prediction at the airport
  where the RNAV (GPS) approach will be flown, and have proper knowledge
  and any required training and/or approval to conduct a GPS-based IAP, may
  file based on a GPS-based IAP at either the destination or the alternate airport, but not at both locations. At the alternate airport, pilots may plan for applicable alternate airport weather minimums using:

Lateral navigation (LNAV) or circling minimum descent altitude
  (MDA);
LNAV/vertical navigation (VNAV) decision altitude (DA), if equipped with and using approved barometric vertical navigation (baro-VNAV) equipment;
RNP 0.3 DA on an RNAV (RNP) IAP, if they are specifically authorized users using approved baro-VNAV equipment and the pilot has verified RNP availability through an approved prediction program.

Note: If the above conditions cannot be met, any required alternate
  airport must have an approved IAP other than GPS that is anticipated
  to be operational and available at the ETA, and which the aircraft is
  equipped to fly.
9.5.1.2 Pilots with WAAS receivers, TSO-C145( ) or TSO-C146( ), may flight plan to use any IAP authorized for use with their WAAS avionics as the planned
  approach at a required alternate, with the following restrictions. When using
  WAAS at an alternate airport, flight planning must be based on flying the
  RNAV (GPS) LNAV or circling minima line, or minima on a GPS approach
  procedure, or conventional approach procedure with “or GPS” in the title.
  Properly trained and approved, as required, TSO-C145( ) and TSO-C146( )
  equipped users (WAAS users) with and using approved baro-VNAV
  equipment may plan for LNAV/VNAV DA at an alternate airport.
  Specifically authorized WAAS users with and using approved baro-VNAV
  equipment may also plan for RNP 0.3 DA at the alternate airport as long as
  the pilot has verified RNP availability through an approved prediction
  program. Code of Federal Regulation (CFR) Part 91 nonprecision weather
  requirements must be used for planning. Upon arrival at an alternate, when the
  WAAS navigation system indicates that LNAV/VNAV or localizer
  performance with vertical guidance (LPV) service is available, then vertical
  guidance may be used to complete the approach using the displayed level of
  service.


text:
Can a commercial pilot get paid by friend?
'm a little bit headache about charge issue with commercial pilot certificate .hope someone help me figure out.

IF my friend approaches to me first and ask for a flight to somewhere using my airplane and I get paid for this flight,am I holding out?If I am,how can I do that legally?How about using his/her airplane?
According to 119.1(e),can I hold out for those flights and get paid(Ferry,banner towing etc.)and get paid？

If your friend approaches you and asks for a one-time ride, you're fine to charge for it. If you decide to advertise, or your friend tells a friend who tells a friend and word of mouth is that you offer an air taxi service, you are holding yourself out as a carrier and need to get a part 135 operating certificate.
Same thing with ferrying, banner towing, etc. If you are offering it to the general public as a service you need to get an operating certificate.

Thank you I got that.What if we decide to fly there every month,just once a month and he(same person each time)pay for me evey time.Is that also fine?Or I have to make a contract with him/her which called private carriage and also need a operating certificate?

Almost positive you don't need an operating certificate for private carriage.

Am I thinking too much?119.23(b)link

If you are doing it once a month you may be pushing the envelope. Do you also need to go to that destination? Then you may be fine, but when the question delves into hazy in-betweens only your local FSDO can answer that question. However, I learned long ago, the hard way, that you don't tell the FAA what they don't need to know.

Your second paragraph is incorrect in the US. 14 CFR §119 explicitly allows you to do these things without an operating certificate. Some of the operations in 119 require a letter of authorization e.g. sight seeing, but none require an operating certificate.


text:
NACA Airfoil 0005.4
I have come across this NACA profile

NACA 0005.4 mod

and it is not clear how to interpret this airfoil. Is this considered a 4 digit NACA profile? What does the number after dot mean?

Yes, it is a valid airfoil identifier. First two zeros indicate it is a symmetrical airfoil with no camber. The next two digits mean it has a five percent thickness to chord length ratio. The number after the decimal indicates a slight adjustment to the maximum thickness and location thereof. Instead of being 5% thick, this airfoil is 5.4% thick. There is quite a bit of very good info on NACA airfoils here. This airfoil is mostly used on helicopter blades, far as I can see.

And the "mod" addition means that is has some arbitrary changes applied to it which make the name almost meaningless. Remember that the Lockheed C-141 also uses a NACA 0013 mod. Heavily modded, with camber and all. The name just meant that Lockheed did not want anybody to know what really has been used.


text:
Is the distance to PNR (point of no return) affected by wind?
Is the distance to PNR (point of no return) affected by wind?
I did research it and found some links, but none discussed about the wind.

How much research have you done? - A quick Internet search shows several useful sites.

Related

I did research. Found some links. But none discussed about this. If you've found one, then please share.

Well, short answer: yes. Intuitively how could the wind not affect the PNR?
But, intuition, especially mine, is sometimes wrong, so let's see. I seem to remember this one from an algebra class, so I took a moment to figure it out. However, my aging brain was obviously going to take a more than a moment (my last algebra class was more than 50 years ago) thus, lazy soul that I am, I went to skybrary.aero and found:

(skybrary.aero)
Let's say we've got 2400 nm to fly in a 500 kt airplane facing a 100 kt headwind. Thus
D = 2400, H = 600, O = 400 and the PNR (ETP) = 1440 nm.
In a no wind situation the ETP (Equal Time Point) would obviously be 1200 nm, so wind does effect the the ETP.
In real life things are not so simple, and flight planning software will take care of calculating such things using winds aloft forecasts along the route of flight as well as other things.

Thank you so much. Apparently my researching skills are not so good.


text:
What are the different vehicle roadways markings?
I was going through the AIM (Aeronautical Information Manual) chapter 2, which talks about airport lights and markings. There are 2 types of lines that designate a vehicle roadway. One is a solid line and the other is a zipper line but I could not understand the difference between the two.

Vehicle Roadway Markings. The vehicle roadway markings are used when necessary to define a pathway for vehicle operations on or crossing areas that are also intended for aircraft. These markings consist of a white solid line to delineate each edge of the roadway and a dashed line to separate lanes within the edges of the roadway. In lieu of the solid lines, zipper markings may be used to delineate the edges of the vehicle roadway.

Are you confused about the difference between a "solid line" and a "zipper line", or the difference in use? if it's just a use question, it appears to me that the answer is in the quote you provided In lieu of the solid lines, zipper markings may be used to delineate the edges of the vehicle roadway. i.e. the airport authority can choose to use either type of line at their discresion.

@FreeMan I'm unable to understand the difference in use.

Based on the snippet you posted, there doesn't seem to be a difference. However, I'm no expert, therefore the comment instead of an answer.

@FreeMan Alright. Thanks for the help.


text:
Why are thermal switches connected in parallel to each others?
Why are thermal switches fire detection system connected in parallel to each others?

Thermal switches, here, are indeed connected all in parallel (Fig. 17-1).
Wiring so allows to trigger the response if any of the switches closes in response to high temperature. This should allow to detect small initial fires that trigger only a single switch, or maybe a couple of them.
The switches are a simple computing machine that performs the logical disjunction.
In the same article you can see thermocouples connected sequentially (Fig 17-2). Thermocouples are not switches, they produce voltage in response to heating, and wiring two of them sequentially in the opposite directions produces the signal proportional to the temperature difference between them. The pair alerts when one thermocouple is heated significantly more than another.

I think I see what the OP is getting at. If the switches act as breakers or fuses you'd want them in series. But if they act to trip a seperate system, as in the diagram on the linked page, then you'd want parallel. So if they are normally open then parallel; if normally closed then series.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
How was the rotation direction decided for single engine propeller craft?
Spitfire, FW-190, Ki-43... was it selected arbitrarily to spin counter-clockwise?

The rotation was decided by the engine manufacturers.

And they didn't always agree... For example, the Genet Major radial engine installed in the C.30 Cierva Autogiro spun 'the other way', counterclockwise as seen by anyone in the propwash...  Another example is the Hispano Aviación HA-1112, a Spanish-built Bf 109 fitted with a Hispano-Suiza engine...

Maybe this was not "decided" at all.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
Is there a Non Directional Beacon(NDB) morse code sound database?
I need to know what is the morse code sound of:
CALL: OZ
Khz: 212
QTH: RUCKR
lat: 31.2292
long:-85.7917
I found this website, but I could not find the sound of different NDBs:
http://classaxe.com/dx/ndb/rna

You can useText-to-Audio Morse generators. Random one: use free text at the end of the page and enter the call sign, here "oz", You can get the corresponding .wav file.

Here’s a website that has some NDB sounds that can give you examples of what an NDB sounds like.
Basically each NDB transmits a one, two, or three letter identification.
On the chart, you can tell what to listen to by looking at the dots and dashes next to the identifier. In the example below, Chualar is UAD
..-
.-
-..

Thank you. I found OZ, 212 in this website https://skyvector.com/


text:
why are turboprop/turboshaft engines rated only in horsepower and never in ft-lbs of torque like diesel engines or electric motors?
I realize torque and horsepower are essentially the same measurement since horsepower is simply torque over time. But I'm curious as to why diesel engines or electric motors always provide torque ratings whereas turboprop engines are only rated in horsepower. Is there any reason for this?

If the turboshaft engine is not in an aircraft, they actually do provide torque numbers. Example AGT1500 (engine of the M1 Abrams) has 3700Nm at 3000rpm.

You’ll even find values for the “chrysler turbine car” from Wikipedia “The 1963 Turbine's engine generated 130 brake horsepower (97 kW; 132 PS) and an instant 425 pound force-feet (576 N⋅m) of torque at stall speed”.

The reason a Diesel engine has a torque figure and a horsepower power figure is because max torque and max horsepower occur at different engine RPMs. Have a look at any performance curves of a piston engine and this will be evident. Hence, to define in a few numbers the maximum performance of the engine, you need to give both figures.
However, turboprop engines for propeller aircraft, and turboshaft for helicopters, operate differently. Maximum efficiency for a rotor or propeller occurs at a certain RPM. Operating at different RPMs is inefficient. Hence, propellers and helicopter rotors are designed to operate at a fixed RPM. As load changes, the blade pitch angle is changed so it “bites” into more or less air. Hence, RPM can be kept constant, despite the load (and hence torque demand) changing. Now, since the power turbine is running at a constant fixed RPM, only 1 performance figure is needed (SHP or TQ) because the other can simply be derived from it.
Torque is just as important in a turboshaft or turboprop as a piston engine. These engines all have a torque sensor that usually works by measuring the twist in the power turbine shaft. Most helicopters do an engine performance check daily that involves reading TQ of the gauge prior to flight to ensure adequate performance.

One can compare it to these 50ccm ICE scooters (like a vespa). There CVT is tuned so that the engine always runs at relatively high rpm, hence delivering nearly max hp. That’s the reason why they can start so fast at traffic lights, despite having only 7kw. The CVT is similar to the self adjusting blade pitch.

Because it's less useful for aviation application.
For diesel and electric, or ground vehicle and industrial motors in general, lack of peak torque is a problem (engine/motor stall), but for aviation, there's never a condition that you can stall a turbine. Usually you stall the propeller way before you stall a turbine.
Or, put it another way, an aviation turbine is rarely found short of torque.
However torque is still an important performance metric and will be stated in the data sheet, but simply isn't actively marketed as much as diesel and electric motor.

Thanks for the answer. But I'm still curious as to why torque would be a more important metric say for a truck engine but less important for powering a low RPM helicopter rotor for example. Wouldn't torque be as important a metric for a turboprop or turboshaft, considering the RPM is low which requires a lot of torque? Maybe I'm just getting confused around the old torque vs horsepower debate.

@ChristophePochari Problem with truck is after you've dropped to 1st gear, or starting with 1st gear, the highest force the wheel can put on to the road is limited by the engine toque. And if the engine can not provide enough torque, then the result is usually very bad (stalling, rolling down hill, or can not start to move at all). For an airplane, as long as the system (prop, gear box) are well designed, the engine never face such difficult situation.

is it possible to compare the power requirements of a truck compared to spinning a prop or rotor?

@ChristophePochari Simply put, there's no minimum torque to spin the prop or rotor - it's going to spin however small the torque (within reason). Static friction is very small, so less torque just means longer spin-up (energy limited) or slower maximum speed (drag limited). This is adequately covered by the power metric.

Torque and horsepower are different measurements.
Horsepower is a measure of power, where one horsepower equals 746 watts.
Torque is a rotational force, which might be akin to voltage.  One can have large amounts of torque, but if a shaft will not turn, no work is done.
Work is accomplished by power.
One may frequently see torque specifications for diesels, because they tend have different operating characteristics.  For example, in common diesel engines, max torque may appear at substantially lower RPMs than on a comparable gasoline (Otto cycle) engine.  With similarly sized gas and diesel engines, the gas engine usually has a higher horsepower rating, and always at a higher RPM.
The torque rating of a diesel engine or an electric motor are merely forces which the device can apply, at a certain RPM.  They are not power ratings.
Horsepower and torque are important attributes when designing propulsion systems, so that the drive requirements (eg. propeller, fan, or wheels on the road) can be matched effectively to the power plant (eg. engine, motor or rubberband).


text:
Would increasing rotor disc diameter increase efficiency in a helicopter by reducing disc loading?
Despite the obvious drawbacks of a larger rotor diameter would the reduced disc loading increase efficiency during hover and forward flight?

you said3
italic Despite the obvious drawbacks italic
you probably should enumerate what the drawbacks you are talking about.Since I don't know which drawbacks you are thinking of, this question now reads
Despite [any possible] drawback, ...
to which the answer must be: hell yea, go fro it baby

Yes, increasing rotor diameter increases efficiency by reducing disk loading, exactly as you say.
From J. Gordon Leishman, Principles of Helicopter Aerodynamics, section 2.3:

..vertical lift aircraft that have a low effective disk loading will require relatively low power per unit of thrust produced..and will tend to be more efficient; that is, the rotor will require less power (and consume less fuel) to generate any given amount of thrust.

Larger rotors means more weight, so the overall loading will be greater /even when/ the larger disk increases airframe's MTOW. So, there's a curve of where rotor blades provide the most lift force for their size (area) and relative airflow- a product of TAS, AoA, and RRPM, all of which can change independently and make blades more or less efficient in different flight configurations (i.e. most efficient at 0kts / 30kts / 80kts, etc...). I assume that the retreating blade stall forward speed reduces with larger blades because the tips of the blades are moving faster, and there's probably much more to take into account...
However, to make things much simpler, all this stuff is all done by the manufacturer, so just slapping larger blades onto your helicopter than what came out of the factory is very likely a very bad idea, and not just from a fuel efficiency standpoint.

Larger rotor means more weight, but it would have to be really humongous before the wait would grow faster than the area. The important thing is that larger rotor means more form drag.


text:
Are solid fuel rocket engines designed differently and how?
How do solid fuel (Hydrazine, UDMH) and oxidizer (N2O4) differ in design from cryogenic rocket engines such as LH2 and LOX?
Are there differences related to temperature, material design, turbopumps, turbopump bearing seals, etc?

This belongs to space.stackexchamge.com.

Hydrazine, UDMH and N2O4 are liquid propellants, not solid.

Yes, solid fuel rockets are very different from liquid fueled rockets. A solid fuel rocket is basically some solidified rocket fuel and oxidizer wrapped in a non-combustible cylinder (hence the name). Once it's lit, there's no way to throttle it or shut it down, it just burns until all the fuel is consumed. On the other hand, in a liquid fuel rocket (cryogenic or not), liquid fuel and oxidizer are pumped into a combustion chamber to be burned. Liquid fuel rockets can be throttled or shut down by controlling the fuel pumps, and can be re-lit once shut down (assuming its igniter is reusable).
(It's important to note that the examples of "solid" rocket fuels you gave aren't actually solids. They're liquids, just like cryogenic fuels are. A solid fuel would be something like the ammonium perchlorate and aluminum powder used in the Space Shuttle Solid Rocket Boosters.)

small addition: it's theoretically possible to have a solid fuel engine that can be throttled. Not sure if it's ever been done, but envision an engine where solid fuels in powder form are fed into a combustion chamber (though at the pressures needed you could probably treat them as liquids in calculations).


text:
What does the XFR button on the Challenger 300's autopilot panel do?
I'm new to aircraft and currently I'm learning the autopilot system of the Bombardier Challenger 300. I saw the "xfr" button but don't understand what it is for. Can someone explain this to me?

You can find manuals for many aircraft including the Challenger 300 at Smartcockpit. The Automatic Flight Control System section includes the function of the XFR button.
There are two flight guidance computer cards that drive the autopilot, including the flight director and yaw damper. The XFR button switches how the computers are used.
For most of the flight, only one computer is use and provides output to both left and right cockpit displays. Pilots will get warnings if this computer fails, and they can push the XFR button to switch to the other one. Without a failure, pushing the XFR button switches so that each side of the cockpit gets input from a different computer.
Precision approach and go-around modes are the exception where by default each side of the cockpit is driven by a different computer.


text:
What is this c. 1930 beautiful monoplane seen in Oakland?
Photo from Denny Wright's album.  He piloted for
Clyde Sunderland.  This photo has no stamp or markings. Anyone recognize this aircraft?

Do you have any more info about the image or Denny Wright himself? Can't really find anything about either.

It looks similar to the Hughes H-1 Racer but the difference is that the H-1's landing gear is further apart and folds towards the fuselage whereas this aircraft's landing gear appears to be non-retractable.

I am going with the Lockhead, due to looks and dates.  The Big plane, right background, is a Western Air Express Folker F-32, NC333N or NC334N (there were two).  The second from the right is Wright's "Whirlwind Waco" (?), NC935K.

Mistake in above comment: the background small monoplane is a "Travel Air six passenger with Wright Whirlwind motor", belonging to Wright Air Service.

I didn't say it was the Hughes H-1. Just that it looked very similar.


text:
Is there any formula that directly relate density to altitude for a wide range of altitude?
I am working on a code to simulate a vehicle trajectory based on forces act on it in different altitudes, I need a formula that gives density in an altitude range between 0 and 40 km to obtain lift and drag in different altitudes. Is there a formula that gives it to me even with a reasonable error?

Without knowing air temperature?

Taking into account the standard air temperature at any altitude

There are the right way and the easy way.

Rigorous way would be to use the ICAO Standard Atmosphere (Doc 7488-CD in 1993) a link for document
Then your code looks for temperature gradient (Table D) and uses eq.12 or 13 for pressure calculation. It depends on the temperature gradient. Then you can easily compute the density eq.14.

Easy way would be calculate density for few altitudes and fit the result with some proper function.

Cheers Robert


text:
Is it possible to predict how busy an airport will be in a given time? (are there existing services that to this?)
I want to know if it's possible to predict how busy an airport will be at a given day or part of day.
I know there are services that provide the scheduled flights in an airport

Is there also an API that allows programmatically accessing this data (preferably for free)
How far in advance are the flights scheduled and the data published?

The distribution between 'regular' passengers and 'connecting' passengers is also important (a passenger during a connection has a much lower effect) - it the data of how many passengers in a flight taking a connection available? (even long term statistics)

I think you need to be more specific as to just what you mean by "busy".  Do you mean planes (not all of which are commercial flights) taking off & landing?  Or do you mean passengers in the terminal building(s)?  Or what?

bottom line - how long you have to wait - but this is probably impractical.
I assume the number of planes leaving \ arriving on a certain time is a good proxy for how busy the airport is

This also depends on "how long you have to wait" for what? Check-in? Security? And which country, etc. In the U.S., Pre-Check can dramatically shorten (or eliminate) time spent in security lines. Having status with an airline or alliance can shorten time spent at check-in.

This is a bit of a different approach than you were thinking, but Google estimates how relatively busy a place is based on location data:

This can be found in the right-side bar if you search for an airport code or many other locations. It's based on their location data, not flight schedules.

Airline dispatchers have that data; I've sometimes gotten info like "destination has 22 aircraft arriving in the 17Z hour (i.e. 1700Z thru 1759Z), with an acceptance rate of 33, so there should be no delays."
If or where this info is available to the public, I don't know. Maybe one of our resident ATC's can add that piece to the puzzle.
This is all about aircraft movements, not passengers, so it isn't necessarily representative of how busy the terminal will be... the tarmac is equally busy whether the 22 airplanes are empty or full.
The "passenger terminal" side of the question would be better suited for Travel.SE than here; I think the Google plot in the other answer is an excellent resource for that aspect.

I don't see how this is predictable, in general.  At larger airports where traffic is in practice limited to scheduled commercial flights, sure, but at many airports the majority of takeoffs & landings are unscheduled private & military planes.

No, not perfectly predictable,  but imperfect data can still be quite useful compared to no data. For military & Part 91 flying,  averages can be useful predictors. And as you note, airline dispatchers care most about the numbers for busy hubs. I don't know to what extent such data is or isn't available for "Podunk Regional" with 8 airlines flights per day. But airline arrivals at such fields aren't really disrupted by local traffic doing touch and go's.

This information is available to the public for many airports in the US and Canada through the Airport Arrival Demand Chart. It can be useful in understanding flight delays if the arrival rate drops (such as due to weather) and a ground delay program is used to hold flights back, but since it's arrivals only, doesn't care how many people are on board each aircraft, and departing passengers arrive on time even for delayed flights, I can't see it being particularly helpful for estimating the wait at places like check-in and security lines.

I believe the business of an airport may be measured with ordinary queue theory.
Googling around I found this  thesis that may answer to your question.


text:
How do the airlines allot the passengers seats to make sure the balance is maintained?
How do the airlines allot the seats for the passengers?
Is there any procedure, like first front seats has to be filled next middle and at last the end seats?
Any algorithm works during the ticket booking to distribute the passengers according to their weight?

Weight is not a factor as the airlines have no idea how big their passengers are.

@GdD there are standard tables to estimate the weight of the passengers. See here: https://aviation.stackexchange.com/a/27943/1467

I'm aware of this @Federico, I'm saying that airlines do not have weight data on individual passengers.

@GdD no, they don't have the exact weight, but "weight is not a factor" is not correct, the weight given by those tables is very much a factor.

I think we are saying the same thing @Federico. Weight is very important, but individual weights of passengers is unknown so they use a value based on known factors.

During seat allocation (which they call "inventory management", airlines are more focused on group seating strategies (families, larger groups) and revenue (cabin partition) than mass balance (which may be tuned by cargo load distribution). Reservation systems may include modules like "seat inventory management" and "load management"

Companies can use also some "load and trim sheets". I also found this: https://www.skybrary.aero/index.php/Aircraft_Load_and_Trim

It depends on the specific limitations of the aircraft and the flight booking load. If the flight is full, it not really an issue. Typically the check-in system will automatically distribute passengers throughout the cabin, starting from the front and moving backwards. Load planners may block rows during check-in if the flight is so empty the center of gravity will be exceeded, unless passengers sit in certain sections of the aircraft.


text:
Does the Reynolds number on a smaller model need to match the one of the original aircraft?
1.Airbus 380-800 :
The overall length of it , is 72.72 m and its cruise speed is 903 km/h. Based on the mean chord of wing , its Reynolds number in cruise phase is around 75 millions. Now , a 1/18 scaled model is built for the purpose of wind tunnel testing. Assuming similar flow condition , the Reynolds number of wind tunnel  tests would be around 4.15 millions. This is great difference. Is Reynolds number , as a very important  similarity variable, is so different for wind tunnel testing comparison  with free flight condition, what is the advantage of performing such tests?
2.do we always need to match Reynolds number exactly?

I have no idea if this is relevant but one thing stands out to me: 903 km/h would be cruise groundspeed, but the wind tunnel would only be testing airspeed.

In wind tunnel testing you need to match several similarity parameters; the most well known are the Reynolds number and the Mach number.
Since the Reynolds number depends on flow speed, viscosity and physical size while the Mach number also depends on flow speed, it looks like both can only be matched when the physical size of the model remains unchanged. But when fluid pressure and temperature are also changed, it is indeed possible to get both close to the real value. This requires an actively cooled, pressurized wind tunnel.
Such tunnels are expensive and have a long waiting list, so other tunnels exist which match both parameters less well. In that case, the researcher needs to pick which is more important and select one of the many facilities in existence.
For preliminary development, it is in most cases sufficient to test at a much lower Reynolds number and then apply correction factors, just as it has been done in the early days of aviation. If, for example, you need to find the lateral stability of a design or test its spin behavior, a smaller Reynolds number is not critical. In order to trip the boundary layer where it would have its natural transition between laminar and turbulent flow, the flight surfaces of such models have artificial roughness applied at the right chord location, so the flow is made as similar as practical.

This will depend on what you are testing for and how accurately you want to test.
It can be sufficient just to match flow regimes. Such that if the actual aircraft has a turbulent boundary layer then your model needs to have one as well. This is easier to do than exactly matching Reynolds numbers.
If the accuracy or type of test demands it you need to match Reynolds and Mach numbers for the model this will ensure your results are the same as they would be in a flight test. In order to match these numbers you will most likely need a pressurized wind tunnel. Or use something like a water tunnel.


text:
What is this abandoned aircraft in Thailand?

A friend found an old photo of himself and an abandoned aircraft in Thailand. Can you identify the aircraft?


text:
Why isn't KTEX's runway designation 10/28 instead of 9/27?
Why is the marking on the runway written as (9/27) Telluride (KTEX), Colorado, USA. whereas the direction is 284 degrees? Shouldn't it be (10/28) instead?

Welcome to Av.SE!


text:
How is the zero-lift drag coefficient calculated?
The drag coefficient is usually given as a funtion of the lift coefficient and the zero-lift drag coefficient ($c_{D0}$):
$c_D=c_{D0}+k\cdot c_L^2$
How can I calculate/estimate $c_{D0}$?

You can look it up in reference books. For wings, the NASA report server is your friend. For complete aircraft, there is some data available in books about pre-design of aircraft. The one I have is Synthesis of Subsonic Airplane Design by E. Torenbeek, and gives the following numbers for $C_{D_0}$

0.014 - 0.020 for high subsonic jet aircraft
0.018 - 0.024 for large turboprops
0.022 - 0.028 for twin engine piston aircraft
0.020 - 0.030 for small single engine aircraft, retractable gear
0.025 - 0.040 for small single engine aircraft, fixed gear
0.06 for agricultural aircraft without spray system
0.070 - 0.080 for agricultural aircraft with spray system

Appendix F of the same book gives a method for more detailed estimation in the pre-design phase, when no wind tunnel data is available, based on data of the components that make up an aeroplane.


text:
How does the propeller position affect the effectiveness of control surfaces?
I've found several questions about differences between pusher and puller aircraft, but the effectiveness of control surfaces was not discussed in any of them.
Consider the following three scenarios:

A: Aerodynamic surface in undisturbed flow
B: Aerodynamic surface with a puller propeller
C: Aerodynamic surface with a pusher propeller

In what case is the lift force generated due to the control surface deflection larger? What differences are there between B and C?

A propeller has more effect on a control surface behind it, than on one in front of it. That's because the propeller pulls in air from a large area in front, and ejects it in a relatively narrow stream behind. Since the mass flow rate is the same on both sides, the air in front moves fairly slowly, and the air behind moves faster. Forces on a control surface in an airflow depend on the square of the airspeed, so a control surface in the fast-moving air behind the propeller will deliver larger forces for a given deflection than one put in the slower-moving air in front. Look up Axial Fan Design on Wikipedia, for a cross-sectional view of the airflow through a propeller.


text:
What happens to an airborne plane when its type is grounded by an authority?
Many countries have (temporarily I think) banned 737 Max 8s from taking off or landing. What happened to the ones in the air? Do they get special permissions or are they forced to divert to a different country that is allowing them to land?

They've been grounded. I don't think that means they can't land. They obviously  have to land.

sudo teleport nearest-airport on-ground

You can find the full wording of the EASA grounding order here which does not specify a course of action for planes mid air but does call for the immediate grounding at the time the order goes into effect (March 12th 2019 @ 19:00Z)

For the reasons described above, pending the availability of more
  information, EASA has decided to suspend all flight operations of the
  two affected models.
This AD is considered an interim action and
  further AD action is expected to follow.

The AD points to sections 301 and 303 of the EASA regulations which does not seem to shed much more light on the situation other than;

Any applicable airworthiness directive must be carried out within the
  requirements of that airworthiness directive, unless otherwise
  specified by the Agency.

Which points us back to the AD, which again offers no specific instructions on immediate grounding.
However according to FlightRadar24's Twitter they are seeing some diversions or at least possible course changes. As people point out in the comments its possible the airlines are diverting the aircraft to airports they can better provide support/maintenance at.

As people point out in the comments its possible the airlines are diverting the aircraft to airports they can better provide support/maintenance at. Many flights originating outside EU and returning to their EU bases were diverted to North Africa and Turkey and the passangers had to be flown by different aircraft on the next day. They planes will probably be allowed to make a technical flight later to the place with support/maintenance available.

authors: Vladimir F Героям слава


text:
Where is fuel metered in continuous flow fuel injection system?
How is fuel metered in continuous flow fuel injection system?

Both questions.

Just in front of the engine. It makes most sense to measure fuel flow as close to the engine as possible: any leaks between meter and engine will distort the measurement. Here is an example of the B737 arrangement.

As to the how, airborne fuel flow meters work in the same way that turbines do: the mass flow of the fuel causes an impeller to spin, rotational speed is then a measure of fuel flow. Note that it is a measure of fuel mass flow, not fuel volume flow: mass flow is not subject to variations due to temperature etc.


text:
What is the best extinguishing agent when wheels catch on fire?
What extinguishing agent must be used in the event of a fire involving wheels/tires? Why?

I don't see the other question as a duplicate. The answers there certainly don't address the issues presented here, such as rubber or metal fire.

You can find some discussion in this thread but what you are looking for is

Fire Service manual. Volume 2. Fire Service Operations : aircraft
incidents Home Office - London
HMSO, 12/99. Crown copyright 1999
ISBN 0-11-341192-8; 0113411928
5.4.2 Brake and wheel fires The overheating of brake and wheel assemblies usually follows excessive braking. This can happen on
  landing when a hydraulic failure reduces the ability of the pilot to
  utilise control surfaces (flaps) and he feels the aircraft may over
  run the runway or more often, on an aborted take-off. Quite often
  tyres will burst or, as the aircraft comes to a standstill, ignite by
  transference of heat from the brakes. To avoid metal failure,
  firefighters attending overheated brake and wheel assemblies should
  usually refrain from applying water and allow natural cooling. If
  there is fire however, a fine water fog applied from fore and aft of
  the undercarriage assembly is generally used.


text:
Why is the Boeing 757 undercarriage so high?
Compared to other wide bodies the 757 seems to stand on very tall landing gear.
Considering strength, weight, cost, stowage space and ease of ground servicing you would want the shortest possible undercarriage you can achieve. The B737 isn't a much smaller aircraft but is much lower, so low it was a challenge to fit modern engines.
Was there a specific design/operation reason or was it just styling - it certainly looks nice !

Indeed it does look nice

The 757 is a narrow-body, not a wide-body (maybe that's what you meant).

Rotation angle at takeoff is often the limiting factor in gear height. The 757-300 is 178ft long, 30ft longer than the Airbus 321 which also has tall landing gear. The first 737s were less than 100ft long, which allowed the short gear and later caused problems with the max9/10 stretches which went to 143ft.

source

The source you provided was incorrect. "http://hhttps//www.jetphotos.com/showphotos.php?aircraft=Boeing%20757-3CQ&airline=all&category=all&country-location=all&genre=all&keywords-contain=0&keywords-type=cn&keywords=32241&photo-year=all&photographer-group=all&search-type=Advanced&sort-order=0&page=3ttp://" is not a valid URL


text:
Can I log the flight as the authorized instructor on board? Commercial long cross country
I was an authorized instructor on board for my students long commercial cross country. Do I log any of that flight time?

were you actively providing instruction? If not, you were a passenger. Whether it'd be legal or not to log that time, unless you were doing the job I'd consider it unethical.

I would expect that if you wee required to be there, you can log it.  It's a long time since I got my commercial, but, the way I remember it, the pilot learning to be a commercial pilot had to do the long cross-country on his or her own.    So I'm having trouble understanding your question.  Unless I did one with an instructor and then one on my own and I'm not remembering correctly.

Answer solved,
https://www.faa.gov/about/office_org/headquarters_offices/agc/practice_areas/regulations/interpretations/Data/interps/2014/Kuhn_2014_Legal_Interpretation.pdf
Short terms, yes.


text:
What does it mean for a GPS PRN to be unserviceable?
There is a current NOTAM:

 !GPS 02/035 GPS Navigation PRN 28 unserviceable Feb 21, 2023 2020Z to May 31, 2023 2359Z

What exactly does it mean for a GPS PRN to be unserviceable, and what significance does it have for navigation?

https://www.gps.gov/technical/prn-codes/

@RodrigodeAzevedo Seems like good info, but I think it assumes I know a few too many things I don't know.

Do you know anything about digital circuits?

@RodrigodeAzevedo Yes.

GPS (Navstar) usually has more satellites in view than are strictly necessary for navigation.   An IFR certified receiver has information to determine when the current computed position is within required specs based on which satellites are in view.   A handheld GPS for hiking may just fall back to an imprecise solution with no warning when insufficient satellites or poor geometry is all that is available.
The protocol used by the system allows up to 32 regular satellites (numbered PRN 1 through PRN 32) to transmit timing information to the receivers used for the location (and another few satellites can transmit WAAS updates).  But the minimum for global coverage is 24.  This means that most of the time, the loss of 1 or 2 satellites doesn't cause a problem.  Aviation users with a clear view of the entire hemisphere should have enough other satellites visible to give good solutions.  Unless there are other problems, I would expect the unavailable satellites to have no impact.
PRN Unserviceable means that this satellite can't be used by your receiver.  Your receiver already knows this.  Most receivers have a page that can display the current vehicles in view, and will display their PRN on the hemisphere relative to your position.
If you have some sort of advanced mission planning that needs to guarantee a specific precision available during an upcoming flight, you could use this information to predict what satellites would be visible, in what geometry, and what the likely precision might be at any point in the flight.  I'm not sure if anyone in civil aviation bothers.

So a PRN number essentially just refers to a fixed GPS satellite? Or do physical satellites switch around PRN numbers?

They can switch.  The PRN is a "logical" number that is reused as sats go into and out of service.  There is also a "SVN" (Space Vehicle Number) that is not reused and isn't limited to 1-32.   (Your receiver doesn't care about that number, just the PRN.)
Status page: https://www.navcen.uscg.gov/gps-constellation

I see, thanks. :)

You answer without even explaining what PRN stands for

@RodrigodeAzevedo Having looked up what PRN stands for, it doesn't seem to add much to the answer. It could just as well stand for "Position Reporting Number" as "Pseudorandom Noise" for all the useful information that conveys. ;)

@Chris Arguably, Gold sequences are one of the most interesting things about GPS. And why can't two satellites use the same Gold sequence if one of them has been decommissioned?

@RodrigodeAzevedo I am interested in that kind of detail. Feel free to write your own answer! I just don't feel there is anything wrong with an answer that focuses on the practical aspects. Adding "PRN stands for pseudorandom noise" alone doesn't add much unless you add a lot more details to go with it.

For a good tutorial on GPS PRN codes, there's this series of articles on Github.

@Gerry Interesting stuff! But it ends on a cliffhanger. :(

These are great questions.  Perhaps ask them in another forum (space?  physics?) and I'll try to address (or in chat...).   But the gory details just didn't seem to be in-scope for Aviation..

oops. You're right. For some reason that page doesn't have a link at the bottom to the following article. Here it is. And that is followed by this article.  There are also this document at the USCG Navigation Center.


text:
Overflying the 100 hour when airplane is not for hire
Suppose I have a 100 hour inspection at 2000 hours total time. From 2100 to 2190 the aircraft is not being operated for hire. If I then have a 100 hour inspection at 2190, when is the next due?

Its good until 2290 on the clock. If you look at the wording of the FAR

(b) Except as provided in paragraph (c) of this section, no person may
operate an aircraft carrying any person (other than a crewmember) for
hire, and no person may give flight instruction for hire in an
aircraft which that person provides, unless within the preceding 100
hours of time in service the aircraft has received an annual or
100-hour inspection and been approved for return to service in
accordance with part 43 of this chapter or has received an inspection
for the issuance of an airworthiness certificate in accordance with
part 21 of this chapter. The 100-hour limitation may be exceeded by
not more than 10 hours while en route to reach a place where the
inspection can be done. The excess time used to reach a place where
the inspection can be done must be included in computing the next 100
hours of time in service.

In other words when you are operating the aircraft in a situation where the 100 hour inspection is required, to be legal for such operations, such inspection had to have occurred at some point in the last 100 hours (or within the last 110 hours if you are flying the aircraft to a location to have the inspection done).


text:
What's this aircraft in the background?
I took this photo from the Wikipedia entry on afterburners. What's the circled aircraft in the background behind the Phantom?

What museum was this photo taken at?

@CarloFelicione Prague Aviation Museum I guess. I cross-reference the list of museums with both a Mig-23 (whose afterburner we are seeing) and a Saab Draken (left).

@DarthPaghius It is the Deutsches Museum (Flugwerft Schleissheim), in Munich

@DarthPaghius the large number of German registrations should be a clue, as well as the SP on the F-4 which indicates the aircraft was stationed at Spangdalem AB in Germany as part of USAFE.

@jwenting It could've been the 'German planes' wing from just about any aviation museum...

@Mast given the sheer number of German registrations, a German museum is most plausible. Take a look at say Duxford and it's mostly UK registrations, Ottawa has mostly Canadian registrations, Lelystad mostly Dutch, it's a recurring theme. Prague would have mostly Czech I presume (never been to that one).

Now that we know the plane is a German prototype it really makes sense for it to be a German museum.

Naturally. Hindsight is 20/20.

The aircraft (I presume you mean what’s visible behind the green F-4 Phantom in the right of the photograph) appears to be a rare surviving prototype of a Dornier Do31 VTOL transport aircraft.

Yeah that's probably it! Looks distinctive enough not be mistaken with anything else.

I've seen this beast in the Deutsches Museum, Museumsinsel in Munich several times in the past. Good to see they moved it indoors.

That spike projecting from the nose of that plane is rather impressive.

@MichaelKaras: first aircraft in history whose primary armament was a tusk. :-)

Seems as trying to use it would be about as deadly as a bee using it's stinger.

authors: Bob Jarvis - Слава Україні


text:
When did the military/Air Force start measuring fuel in pounds instead of gallons?
Watching a training film for the B-47 from 1951, they mention (around 12:30) that the fuel is now measured in pounds instead of gallons on the instruments.   Was that a new concept with jet aircraft?  Did previous propeller aircraft instruments always measure gallons instead?

I don't think it's just military that measures fuel in pounds - I believe everyone does it. (Except for those who measure in kilograms, of course.)

Good question! It makes sense for the conversion to have been done in 1951, as the film you saw states, because that is the year when JP-4 fuel was introduced. JP-4 has a lower freezing point (-60C) than earlier JP-x fuels, which were all derivatives of JP-1, first introduced in 1944. Lower freezing point means the aircraft can fly higher, and the changes in volume would have led to the change in measurement basis.
The reason is that the weight of fuel doesn't change with temperature or pressure, but the volume does. Rule of thumb is about one percent change in volume for every ten degrees centigrade up or down.
A little experiment to prove this would be to weigh a glass of water, cool it in the freezer for a few hours, and weigh it again.
If fuel quantity indicators on jet aircraft were based on volume they would indicate different levels depending on the aircraft's altitude and outside ambient temperature. That would not be very useful.
It does also make weight and balance calculations easier, otherwise the loadmaster would have to compensate for temperature when calculating center-of-gravity.

While the information in this answer is useful, I believe the OP is asking about when as in what year / decade, and the question is tagged with "aircraft history"

As @kevin says, while this is great information it answers the question of “why” not “when”

Just as a matter of information, weight & balance software does typically compensate for temperature when calculating the c.g. I ran a quick test putting 344,000 lb of fuel into an empty 747-400. The results at 6.43 lb/gal, 6.7, and 7.1 were a zfw c.g of 14.3% mac, 15.5%, and 16.9% respectively. The c.g. of the filled portion of a tank changes with volume, and since the fuel volume is temperature dependent. a tank c.g. is temp dependent, and hence the aircraft c.g. is temp dependent. The 6.43 and 7.1 values are the minimum and maximum fuel densities allowed for the 747-400.


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aircraft display Processors
what kind of Processors and GPU are used for Aircraft display ? Is it possible to use single processor to run all three displays (Primary flight display, Navigation display and EICAS)?

Rockwell Collins Pro Line Fusion, the current state of the art, adopted the Radeon E2400 in 2012 to drive the displays (that's pretty new by aviation standards).
There is no way that a single processor would be used to drive multiple displays as that kind of single-point-of-failure possibility for that level of criticality is simply not allowed.
The older cathode ray tube stuff will use processors from the 80s, like the 286.

Airplanes have a long history of evolution, and so do computers.
But some latest developments seems to suggest that, yes, people are working on it to use a single computer system to display and control everything, but right now the innovation front is in the automotive industry where regulatory complexity is lower.


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Can we change light aircraft skin from aluminum to foam and fiberglass?
Can we change the skin and wings of light aircraft from aluminum to foam and fiberglass composite in zenith ch 750 ?

Yes. No. A little bit of yes, but overwhelmingly a NO.
It's possible to design and build an aircraft like the CH-750 with fiberglass instead of aluminum, but it's so far above the skill and qualifications of anyone who would ask the question on the web - as opposed to starting by modeling it in ANSYS - that the only realistic answer is "no".
Not because of any intrinsic properties of fiberglass, but simply because of the level of knowledge involved in redesigning an aircraft of this scale, and the fatal consequences of getting it wrong.

Possibly.  The right foam, the right resins, the right fiberglass or better fiber such as carbon fiber, layered and cross braced in the right way.
Done wrong, the least of your problems could be a wing that is heavier than the original.
It's not an automatic win, you can't just lay up an aluminum shape in fiberglass and call it a day.  It needs to be re-engineered based on all the properties of the new material.  Ask anyone who's re-decked a wood sun-deck with Trex!
Foam doesn't have any particular strength.  It is just a filler / shape-holder to hold the composite in the right shape while it cures.  It does help the composite stay where it belongs, but not much - that would depend on tensile or compressive strength of foam, and that is laughable, especially over years.
On something like a boat, which requires ballast to even hit its minimum desired weight, you just leave the foam or wood "forms" in place for life.  This is also done in house construction using foam molds for concrete; the foam is left in place for insulation value and ease of attaching siding/drywall.
Where weight matters, one effective strategy in composite fabrication is to use a foam that dissolves in a solvent that does not attack the composite, e.g. The way gasoline will dissolve polystyrene but not some epoxy resins.  Then wash out the finished product in the solvent, causing the foam to dissolve.  In a modern industrial environment that would be recovered, separated and reused.  This sort of thing is already done at foam-cup plants, which use pentane as a blowing agent for polystyrene.

I would also check into the weight of the resulting structure.  Foam is disappointingly heavy and weak compared with cantilever balsa (and air spaces) construction. Epoxy and fiberglass can be used to reinforce key areas such as wing roots.  But stressed skin over a metal framework is a time honored aircraft construction method.
Light carbon composites (technically including wood) are making inroads for future designs
as they offer considerable strength that foam does not have and corrosion resistance that metals lack.
Layers of different types of materials are famously used in Mongol bows and show how something like a wing could be built to be both strong and flexible.  Plywood is another example.
One thing about aluminum is the thinness of the sheets that fiberglass would have difficulty matching.  Weight savings is crucial in aircraft.


text:
Need more volume with my aviation headset (David Clark OneX). I wear hearing aids
Does anyone know of a way to get more volume out of my David ClarK ANR aviation headset.  I wear hearing aids and often fly in older airplanes with older radios that are scratch/weak/etc.  I select full volume but still have trouble hearing the communications.  Is there any inline booster or something like that?  Thanks....larry

Is the volume on the radio unit and if installed, intercom unit, all turned up all the way? There are often multiple sources of volume control on the chain, if all are turned up all the way you can get quite a bit of gain out of the system.

There are hearing aids which have a bluetooth input. While this is not fixing the cause, but the effects, this could be a lead to follow if the audio system can be streamed using bluetooth.

Disagree with the on-hold call. Headsets and comm's are a big part of aviation, talking with ATC is an importan part of flying.

I also disagree, as the use of headsets has been an important aspect of improving flight communications and safety in aviation.

A suggestion would be to employ a portable intercom, and use it just for the headset where the higher audio level is desired.  The portable intercoms generally have an amplifier which can drive 4 headsets and often gives another 15 to 20 db headroom.  You may have to try a few different intercoms to assure that the one you are interested in has enough gain.  Also, if you had a frequency shaping circuit (have a student who needed one for hearing deficits) you could provide equalization to optimize intelligibility without affecting others who plug into the aircraft intercom/audio. Will post if..

This is a decent article to take a look at but you may want to consider the clarity aloft headsets which use hearing aid speakers and seem to be able to serve as a nice drop in replacement.

I have a hearing loss. Can I use this headset with my hearing aid?
Because our headset uses high quality hearing aid speakers, the pilots
  who have hearing impairment just remove their existing hearing aids
  before putting on our headset. A balance control can be adjusted to
  favor one ear with louder sound. We have many pilots who have a range
  of hearing problems from mild to moderate.